Cable Materials Research Articles

Vulcanization kinetics and mechanical properties of filled ethylene-vinyl acetate copolymer rubber composites

Abstract The vulcanization reaction of ethylene vinyl acetate copolymer (EVM) rubber is fast, resulting in poor processing safety. EVM is often filled with flame-retardant fillers as insulating or sheathing material for wires and cables. Herein, the effects of flame-retardant magnesium hydroxide (Mg(OH)2), aluminum hydroxide (Al(OH)3) and of the traditional reinforcing fillers carbon black (CB) and silicon dioxide (SiO2) on the vulcanization kinetics of EVM were investigated. The vulcanization characteristics showed that the scorch time (T 10) of the unfilled EVM (KB), SiO2/EVM, Mg(OH)2/EVM, and Al(OH)3/EVM composites was about 1.75 min. T 10 of the CB/EVM composite was 2.22 min. Compared with KB, the activation energy (E a ) increased by about 15 kJ/mol for CB/EVM composites and by about 5 kJ/mol for SiO2/EVM, Mg(OH)2/EVM and Al(OH)3/EVM composites. The results indicate that CB delays the vulcanization time of EVM rubber, slows down the rate of vulcanization reaction and improves the safety of vulcanization. The addition of SiO2, Mg(OH)2 and Al(OH)3 has little effect on the vulcanization reaction. The mechanical properties show that CB/EVM is more uniformly vulcanized and has the best mechanical properties with a tensile strength of 17.61 MPa and elongation at break of 404.58 %. Mg(OH)2/EVM and Al(OH)3/EVM samples have prominent vulcanization non-uniformity resulting in poor mechanical properties.

Effect of zinc oxide nanoparticle size on the dielectric properties of polypropylene‐based nanocomposites

AbstractTo develop new environmentally friendly and recyclable high‐voltage cable insulation materials, the effects of the particle size of zinc oxide (ZnO) on the mechanical and electrical properties of nanocomposites were investigated based on a feasibility study of polypropylene (PP) as a high‐performance cable insulation material. The small particle size of ZnO can synergistically toughen PP with a polyolefin elastomer (POE), but the large particle size of ZnO leads to lower elongation at break. Adding ZnO nanoparticles can improve the bulk resistivity of the composites and suppress space charge injection. 0.5ZnO200 has the highest direct current and alternating current breakdown field strengths, 36.6% and 14.7% higher than PP/POE, respectively. This improvement may be due to the ability of 200 nm ZnO to introduce more deep traps. However, as the nanoparticle content rises and the particle size decreases, the agglomeration becomes more frequent, leading to the overlap of inter‐nano interfaces and reducing the modification effect of the nanoparticles. This study on the effect law of nano‐ZnO with different particle sizes on the microstructure, mechanical properties, and electrical properties of PP can provide a reference for developing new recyclable high‐voltage insulated cable materials.

Theoretical study on the reaction mechanism of a new XLPE insulation material without cross‐linking byproducts: An alternative to peroxide cross‐linking

AbstractObjectiveDesign a new cross‐linked polyethylene (XLPE) insulation material without cross‐linking by‐products (an alternative to peroxide cross‐linking). Investigate the process of covalent bonds forming and reaction mechanism of four reaction systems.MethodTheoretical calculation of the reaction potential energy information of the eleven reaction channels is used density functional theory at B3LYP/6‐311+G(d,p) level.ResultsThe calculation results show that the epoxy and reactive functional groups between two poly‐ethylene copolymers can react in situ, form covalent bonds, and realize a network XLPE. This reaction process is cross‐linking byproduct‐free. The reactivity of carboxylic acid functional group is stronger among four reaction systems considered.DiscussionThe reaction Gibbs energy barriers of synergistic reaction are lower than that of step by step reaction. The reaction channel of attacking tertiary carbon site CH on epoxy is more kinetically favorable than that of attacking secondary carbon site CH2 on epoxy.ConclusionThe cross‐linking of epoxy and reactive functional groups between two polyethylene copolymers in situ would be beneficial to avoid forming cross‐linking byproducts of peroxide cross‐linking process, which is a promising method for design thermoplastic insulation materials for power cables.

Neural network based prediction of the efficacy of ball milling to separate cable waste materials

Material recycling technologies are essential for achieving a circular economy while reducing greenhouse gas emissions. However, most of them remain in laboratory development. Machine learning (ML) can promote industrial application while maximising yield and environmental performance. Herein, an asynchronous-parallel recurrent neural network was developed to predict the dynamic behaviour when separating copper and poly(vinyl chloride) components from the cable waste. The model was trained with six datasets (treatment conditions) at 3600 epochs. High accuracy was confirmed based on a mean-square error of 0.0015–0.0145 between the prediction and experimental results. The quantitative relationship between the input features and the separation yield was identified using sensitivity analysis. The charged weight of cables and impact energy were determined as the critical factors affecting the separation efficiency. The ML framework can be widely applied to recycling technologies to reveal the process mechanism and establish a quantitative relationship between process variables and treatment outputs.

Application of Magnesium Hydroxide/Diphenoxy Phosphate in Silicone Rubber Flame Retardant Cable Material

Deketoxime–type room–temperature vulcanized silicone rubber cable materials were prepared using α, ω–dihydroxy polydimethylsiloxane, carbon black, calcium carbonate, magnesium hydroxide, piperazine bis (diphenoxy phosphate) salt (PBDP), and melamine diphenoxy phosphate (MDP). The effects of carbon black and flame retardants on the mechanical properties, flame–retardant properties, and electrical insulation properties of silicone cable coatings were investigated. The research results showed that the products obtained had good mechanical and electrical insulation properties, with tensile strength greater than 3.0 MPa, dielectric strength greater than 22 kV/mm, and volume resistivity higher than 6.5 × 1014 Ω·cm. When 30 parts of Mg(OH)2:MDP = 2:1 are added to 100 parts of resin, the flame–retardant performance of wire and cable materials can be significantly improved. Under the thermal radiation illumination of 50 kW/m2, the ignition time (TTI) of the Mg(OH)2/MDP coating increased by 16 s, and the maximum heat release rate (pkHRR) and total heat release rate (THR) decreased by 29.7% and 68.8%, respectively, compared with silicone rubber without flame retardant. The silicone rubber coatings prepared were flame retardant up to the FV–1 level.

Aging Analysis of Cable Insulation Material by Terahertz Time-domain Spectroscopy

Insulation materials with high sealing, high insulation, high elasticity, and other characteristics are widely used in the power industry. In this paper, the terahertz time-domain reflection spectrum of cable insulation materials is studied, the optical parameters of cable insulation materials are extracted to characterize the aging state of cable insulation materials, the terahertz time-domain reflection signal of insulation materials with different degrees of aging is tested, and the terahertz reflection spectrum of insulation sheaths is analyzed. The relationship between the aging degree and absorption coefficient in terahertz time-domain spectral reflection mode is obtained. There are obvious differences in the absorption characteristics of cable insulation materials with different degrees of aging in the terahertz band. The longer the aging time is, the greater the absorption coefficient is and the lower the refractive index is. Terahertz time-domain reflectometry plays a role in cable protection with high detection accuracy in the characterization of cable insulation materials.

A Novel Condition Assessment Method for Corrugated Aluminum Sheathed XLPE Cables Based on Evolved Gas Analysis

Condition assessment is significant to the maintenance management of high-voltage cross-linked polyethylene (XLPE) power cables. This paper presents a condition assessment method for corrugated aluminum sheathed cables based on evolved gas analysis. First, simultaneous thermogravimetric and mass spectrometric analyses of the pyrolysis of each cable material were conducted to characterize the gas generation caused by thermal faults. Simulated experiments were designed to investigate gas generation caused by electrical faults. The results show that different cable faults (low and high-temperature pyrolysis of semiconductors, insulation, and buffer materials; low and high energy discharge activity across insulation materials and electrochemical corrosion of the buffer material) show distinct gas generation characteristics. Based on the evolved gases, a method of identifying faults from the key gas concentration is proposed in this study. Moreover, gas transport within the corrugated aluminum sheathed cable with a buffer layer was analyzed, based on which a gas sampling method for cables with a buffer layer is proposed. Finally, the developed method was validated by practical applications. The proposed method is comparable to conducting a blood test on a human body in that it can help discover various incipient cable faults. The fundamentals and data interpretation methods are adaptable to all XLPE cables.

Application Assessment of Electrical Cables during Smoldering and Flaming Combustion

Electrical cables are a potential source of ignition and fire hazards in various types of buildings and industrial installations, as well as in all modes of transportation, including aircraft. Fires in buildings pose the greatest threat to human life and health. The composition of thermal degradation products depends mainly on the type of combustible materials and the type of combustion process—flaming or smoldering. The purpose of this paper was to determine, based on experimental studies, the effects of flaming and smoldering combustion on the response times of fire smoke detectors. In addition, the concentrations of fire gases formed in the process of duct combustion, including CO, SO2, NO2, NO, HCN, HCl, HBr and HF, were measured using an FTIR spectrometer. The results presented confirm the significant effect of the way the cable samples burned on detector tripping time. The highest concentration of smoke (Y) in the test chamber was obtained during flame combustion. It was further found that the characteristics of the cable insulation material used, such as the type of PVC, had a significant effect on the toxicity of the emitted gases. The largest amounts of toxic gases were emitted during the smoldering combustion of a cable with a plasticized PVC sheath.

Free Vibration of Inclined Twisted Cables

This paper is aimed at simulating and investigating the coupled translational and rotational vibrations occurring simultaneously in inclined sagged cables. The three-dimensional behavior of the single-layered six wires strand stiffness results are reduced to effective one-dimensional behavior from the elasticity-based finite element behavior analyses under axial tension and torsional loads. These are directly compared with multiple one-dimensional analytical model results. The effective stiffness coefficients agreed well for the actual lay angle of the cable and at angles below 20 degrees with finite element models where internal contact was not considered. To find the cable natural frequency and corresponding modal shapes the derived primary stiffness and mass matrices are discretized over the inclined sagged cable using a finite element model where the two-node cable element has three translational and three rotational degrees of freedom. The vibration behavior is also studied using extensive experimental tests using the same cable geometry and material used in the numerical calculations. In addition to the physical experiments, the finite element model accuracy was also compared with results from a well-known analytical model available from the literature for horizontal cables, and the influence of the inclination angle variation was also investigated and compared with the computer finite element software ABAQUS for the same purpose. The results found confirm the correctness of the derived formulation, mathematical, and psychical importance of the six-degrees of freedom finite element model developed and the efficiency in evaluating the coupled cable dynamic behavior. It addition, the results highlight the fundamental dynamics of inclined cables and the role of the inclination angle, sag, and weight of the cable.

Microscopic Mechanism of Electrical Aging of PVDF Cable Insulation Material

In this study, the quantum chemical method was used to investigate the microscopic characteristics of α-poly viny difluoride (PVDF) molecules under the influence of an electric field, and the impact of mechanical stress and electric field polarization on the insulation performance of PVDF was analyzed through the material's structural and space charge characteristics. The findings reveal that long-term polarization of an electric field leads to a gradual decline in stability and a reduction in the energy gap of the front orbital, resulting in the improved conductivity of PVDF molecules and a change in the reactive active site of the molecular chain. When the energy gap reaches a certain value, a chemical bond fracture occurs, with the C-H and C-F bonds at the ends of the backbone breaking first to form free radicals. This process is triggered by an electric field of 8.7414 × 109 V/m, which leads to the emergence of a virtual frequency in the infrared spectrogram and the eventual breakdown of the insulation material. These results are of great significance in understanding the aging mechanism of electric branches in PVDF cable insulation and optimizing the modification of PVDF insulation materials.

Influence of Friction Coefficient between Cable and Membrane on Wind-Induced Response of Air-Supported Membrane Structures with Oblique Cable Net

Cable-membrane constructions typically exhibit significant displacement and distortion under load action, and the cable-membrane contact results in relative sliding. In this paper, the interaction force between cable and membrane is transferred through frictional contact action, and as a result, the friction coefficient must be taken into consideration for the form-finding and load analysis of air-supported membrane structures. Eight kinds of P-type membrane materials commonly used in engineering were chosen, and the friction coefficients between the various membrane and cable materials were obtained. The connection between a cable and a membrane of an air-supported membrane structure is considered a contact problem, and its initial shape analysis and wind load response analysis are carried out. The influence of the friction coefficient of a cable membrane on the wind-induced response of an air-supported membrane structure is discussed, and the results are compared with those of the cable-membrane binding model under wind load.

Influence of Thermal Aging on Dielectric Properties of High Voltage Cable Insulation Layer

Thermal aging is one of the main reasons for the degradation of insulation properties of high voltage cable. Dielectric properties and breakdown strength are important parameters to reflect the insulation performance of the cable insulation materials. In the work, the influence of thermal aging on dielectric and breakdown performance of the cable insulation layer was studied. Firstly, XLPE cable insulation samples were prepared and the thermal aging treatment was carried out. Secondly, the microstructure and molecular structure of XLPE samples under different thermal aging time were analyzed. The dielectric properties and breakdown characteristics of XLPE samples under different thermal aging times were characterized in macro aspect. Finally, the effects of different temperatures on the molecular microstructure of XLPE were studied. The results show that with the extension of thermal aging time, the microstructure of XLPE molecule is destroyed, the macromolecular chain is gradually cleaved, and the carbonyl absorption intensity increases. At power frequency, the breakdown strength decreases from 75.37 kV/mm to 62.18 kV/mm, the relative permittivity increases from 2.44 to 2.51, and the dielectric loss increases from 1.47 × 10−4 to 3.10 × 10−3. The free volume rate of XLPE molecules increases with the increasing temperature, and the mean square displacement gradually increases. The work has good guiding significance for the safe operation and condition assessment of high-voltage cables.

Temperature mapping model of cables considering the coupling of electromagnetic and thermal field

Background: During cable operation, its internal temperature reflects the actual working condition of the cable. Once overload occurs, its conductor temperature will rise rapidly. Under high temperature conditions, the insulation material is very prone to breakdown accidents, which seriously threatens the safety of the power system. Methods: To reflect the actual operating condition of cables with high fidelity, a cable temperature mapping model is proposed with the coupling of electromagnetic and thermal field taken into consideration. Firstly, a finite element model is formulated based on the cable structure and material parameters. Secondly, the coupling between electromagnetic and thermal field is analyzed, and multiple coupling calculations are performed iteratively according to the operating conditions. Finally, the mapping between temperature and current flowing through the cable is established to accurately reflect the variation of cable’s internal temperature under different operating conditions. The cable surface temperatures under five operating conditions are measured online and compared with the calculated results of the temperature mapping model. Results: The absolute error between the calculated value of the model and the actual measured value is 0.88°C and the relative error is 1.46%. Conclusions: The temperature mapping model developed in this paper can accurately calculate the internal temperature of the cable and forms an important part of the digital twin model of the cable.

On the pyrolysis characteristic parameters of four flame-retardant classes of PVC sheathless cable insulation materials

Flame retardant cables are widely used today, while the comparison of thermal degradation behavior between PVC cable insulation materials with different flame-retardant levels has not been extensively studied so far. The thermal degradation behaviors of four flame-retardant and one non-flame-retardant PVC cable insulation materials were studied using thermogravimetric (TG) analysis and a combination of TG-Fourier transform infrared analysis. Generally, TG data differ at the first peaks but are similar at the second peaks for various types of insulation materials. This is because the reaction mechanisms of the first pyrolysis stage vary with the change of flame-retardant level, while the second pyrolysis stage is similar regardless of the flame-retardant level. Besides, the flame-retardant performance level cannot solely be evaluated based on the activation energy of these insulation materials. The coupled Fourier transform infrared spectroscopy (FTIR) shows that during the pyrolysis of flame-retardant PVC insulation materials (ZA-BV, ZB-BV, ZC-BV, and ZR-BV), the amount of the seven major released components, arranged in order from most to least, is C-H bending > H2O > C-H stretching > CO2 > C-H aliphatic bending > CH2 deformation > C-Cl stretching. While for the non-flame-retardant PVC insulation material (BV), the series is CO2 > C-H bending > C-H stretching> H2O > C-H aliphatic bending > CH2 deformation > C-Cl stretching. The reported results provide a basis to evaluate the thermal degradation behavior of typical PVC cable insulation materials at present and can also provide essential data for the numerical simulation of an electrical fire.

Study on high-temperature and high-voltage insulation characteristics of polypropylene blend with highly packed elastomeric domains for power cable applications

In this paper, we report the high-temperature and high-voltage (HV) insulation characteristics of the polypropylene (PP) blend with highly packed elastomeric domains that showed excellent mechanical toughness in our previous study to find its suitability as insulation material for power cable applications. The main focus lies on tensile properties with thermal aging, thermomechanical behavior corresponding to the thermal transition, high-temperature volume resistivity and DC dielectric strength, and space charge accumulation behavior of the PP blend in comparison to the crosslinked polyethylene (XLPE). Our PP blend having low elastic modulus of approximately 266.9 MPa exhibited high tensile strength and elongation at break, and high-temperature stability as well. Using this PP blend, not only good HV insulating performances in volume resistivity and DC breakdown strength (BDS) were obtained similar to XLPE, but also adequate values were obtained at high temperature, even at 110 °C, which was not possible with XLPE. However, there was space charge accumulation and electric field distortion in the PP blend like XLPE, which needs to be suppressed. Therefore, our PP blend is expected to have the potential to replace existing XLPE as insulation materials for future HV power cables.

Enabling High-Performance Polypropylene Nanocomposites With Interfacial Deep Traps

Polymer nanocomposites are the material of choice for dc insulation. The emerging demand for high-capacity high voltage direct current (HVdc) power transmission requires polymer nanocomposites capable of safe and stable operation at high temperatures. However, the high-temperature electrical properties of current polymer nanocomposites are still unsatisfactory. Here, we report that the modulation of polymer/nanoparticle interfaces can greatly improve the high-temperature insulation properties of polypropylene (PP)-based nanocomposite for recyclable HVdc cable insulation application. The nanoparticles are surface-modified with PP-graft-maleic anhydride (PP- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${g}$ </tex-math></inline-formula> -mah), which is not only well miscible with PP but also contains polar groups to act as interfacial deep traps. We demonstrate that the interfacial deep traps can improve the dc breakdown strength and the electrical resistivity of polymer nanocomposite by inhibiting the charge injection. This work deepens the understanding of interfacial effects in polymer nanocomposites and provides new opportunities for designing high-performance recyclable insulation materials for HVdc cables.

Magnetic Shielding for Electric Car Power Cables

In this article, the effect of different magnetic shielding materials for electric car power cables has been studied using finite element analysis (FEA), verified by experimental results. Bearing in mind the complex spectrum modulation, typically using pulsewidth modulation (PWM), a magnetic field shielding up to 2 kHz is required. Therefore, magnetic shielding was studied for frequencies of 2 kHz, 50 Hz, and dc field. The employed magnetic shielding materials were high permeability layers, such as permalloy, as well as composites based on resin matrix including flakes or powders from nanocrystalline ribbons, such as nanocrystalline FINAMET ribbons. Magnetic shielding was studied for cable illustrating good shielding ability using a combination of Cu and permalloy sheets for frequencies up to 2 kHz. Furthermore, magnetic shielding was studied for the case of floor shielding, where permalloy appeared to be an acceptable shielding solution.

On The Flame Behavior during Cable Insulation Material Ignited by Fault Arc: A Flame Extracting and Noise Reduction Algorithm

The electric fault arc, particularly the series arc, leads to plenty of electrical fire. The limitations of t previous studies include: (1) most existing research focused on gaseous atmospheres rather than solids materials, which is contrary to the actual demand; and (2) the studied external heat sources were restricted to cone heaters and flames, while the electric arc was seldom studied. To overcome these limitations, we developed an experimental platform to investigate the flame behavior when cable insulation material was ignited by the fault arc. We proposed a flame-extracting and noise-reduction algorithm to process the enormous number of photos shot by the high-speed camera. The main obtained findings were: (1) the appropriate size of the structuring element plays an essential role in filtering the flame region in the photos, too small a size resulted in the wrong recognition of incandescent particles, while too large a size made a jagged distortion; (2) the mean flame area increased as the system load grew; (3) The flame size became more prominent, and the flame appeared more frequently in specific locations when the system load increased. The in-depth understanding of flame behavior provided by this work will help to optimize the design of electric systems and disaster prevention reduction.

Electric field regulation of polypropylene insulation for high voltage DC cables

High voltage cable is the key factor to determine the quality and capacity of power transmission. Polypropylene has widely attracted more attention because of its excellent heat resistance, insulation and green environmental protection, and it is used as cable material. Polypropylene insulation material for high voltage cable needs to bear pulsed voltage and the DC rated voltage, which can easily cause electric field to be distorted and lead the space charge to be accumulated. Meanwhile, the change of cable temperature will also affect the conductivity of insulating material and promote the accumulation of space charge, resulting in the distortion of internal electric field of insulating material and the initiation and growth of electric tree. Therefore, it is necessary to regulate the electric field of high voltage cable so as to suppress the deterioration phenomena such as electric field distortion, partial discharge and electrical demoralization. In this work, the theory and method of regulating DC electric field of polypropylene insulation of high voltage cable is first introduced. Then the main direction of electric field regulation is presented. Finally, the application prospect of polypropylene cable insulation is also put forward.

Numerical analysis of the mechanical and electrical properties of CORC cables under torsional loading

The type II high-temperature superconducting (HTS) ReBCO tapes have been widely used in high-field magnets. Conductors on round core (CORC) cables can carry very high currents in background magnetic fields exceeding 20 T, making it one of the most important types of HTS cables. However, the cables of the magnets in the fusion reactor are subjected to large mechanical and electromagnetic loads that may twist the CORC cables. The intrinsic strain of the superconducting cable is constrained by the brittleness of the HTS tape, which, if exceeded, will cause irreversible damage by producing cracks in the ReBCO layer. A finite element (FE) model was developed to predict how the CORC cable will perform in torsional cases. A comparison of numerical simulations with experiments for a single- and double-layer CORC cable is first performed to validate the model's reliability. For single-layer CORC cables, our model reduces the error between FE results and experiments from 46.7% to 6.7%. Variations in the winding angle, tape width, Poisson's ratio of the CORC cable core material, and core radius were made as part of the parametric analysis. The critical torsion angle is analyzed from the perspective of critical current density reduction. The results show that maintaining a small tape gap (smaller winding angle (26−30°), smaller core diameter, and larger tape width) and a small Poisson ratio can improve the strain limit of the ReBCO layer. The reason for the plateau phenomenon in the normalized critical current density curve of the double-layer CORC cable is reinterpreted. It is also confirmed that multi-layer CORC cables still need to maintain a small tape gap. The FE model can guide optimizing a cable design for specific application conditions.